1. Field of the Invention
The present invention relates to a method of producing a Bi-Pb-Sr-Ca-Cu oxide superconductor, and more particularly, it relates to an improvement for attaining high critical current density.
2. Description of the Background Art
A specific material exhibits diamagnetism under a superconducting phenomenon such that no potential difference is developed although a finite stationary current flows in its interior.
This superconducting phenomenon is applied to an extremely wide range of fields such as that of electric power including MHD power generation, power transmission and magnetic energy storage and that of transportation including a magnetic levitation train and an electromagnetically thrust ship. Further, a high-sensitive sensor for a magnetic field, a high frequency, radiation or the like utilizing the superconducting phenomenon is applied to the field of measurement, and also superconductors are used in the field of nuclear magnetic resonance (NMR), .pi.-meson remedy and a high energy physical experimental apparatus, while the superconducting phenomenon is also expected in the field of electronics, represented by the Josephson device, as a technique which can not only reduce power consumption but implement an element of extremely high-speed operation.
Superconductivity was until recently only observed under a very low temperature. Even Nb.sub.3 Ge, which has been referred to as that having the highest critical temperature T.sub.C of superconductivity within conventional superconducting materials, has an extremely low critical temperature of 23.2 K, and this value has been regarded as the limit critical temperature of superconduction for a long period of time.
Therefore, a superconducting material has been generally cooled to a temperature below the aforementioned critical temperature with liquid helium which boils at 4.2 K, in order to implement a superconducting phenomenon. However, such employment of liquid helium leads to technical and economic burdens due to cooling equipment including liquefaction equipment, to hinder implementation of the technique of superconductivity.
On the other hand, it has been recently reported that a composite oxide sintered body can show superconductivity at a high critical temperature, and development of the technique of superconduction is abruptly being prompted with a superconductor whose critical temperature is not very low. It has been reported and recognized that a Y-Ba-Cu-O material superconducts at 90 K while Bi-Sr-Ca-Cu-O and Bi-Pb-Sr-Ca-Cu-O materials superconduct at 110 K respectively.
Liquid nitrogen is relatively easily obtainable at a low cost, and in fact, development of the technique of superconduction has been greatly advanced with discovery of a superconducting material which operates at the temperature of liquid nitrogen.
However, not only the critical temperature but current density is an important matter of concern for a superconducting magnet, a wiring member for a device, a power cable or the like in practice, such that current density of at least 1000 A/cm.sup.2 must be attained. When the superconductor is elongated, further, such current density must be substantially uniformly attained over the longitudinal direction of the elongated superconductor. The critical temperature can be increased by using a Bi superconductor or a superconductor containing Bi which is partially replaced by Pb in particular, while current density of such a Bi superconductor is 100 to 200 A/cm.sup.2 at the most. In practice, however, the current density must be ten times or more, while such high current density must be substantially uniformly attained over the longitudinal direction of the elongated superconducting material.